Modeling Longitudinal Preclinical Tumor Size Data to Identify Transient Dynamics in Tumor Response to Antiangiogenic Drugs.

Experimental evidence suggests that antiangiogenic therapy gives rise to a transient window of vessel normalization, within which the efficacy of radiotherapy and chemotherapy may be enhanced. Preclinical experiments that measure components of vessel normalization are invasive and expensive. We have developed a mathematical model of vascular tumor growth from preclinical time-course data in a breast cancer xenograft model. We used a mixed-effects approach for model parameterization, leveraging tumor size data to identify a period of enhanced tumor growth that could potentially correspond to the transient window of vessel normalization. We estimated the characteristics of the window for mice treated with an anti-VEGF antibody (bevacizumab) or with a bispecific anti-VEGF/anti-angiopoietin-2 antibody (vanucizumab). We show how the mathematical model could theoretically be used to predict how to coordinate antiangiogenic therapy with radiotherapy or chemotherapy to maximize therapeutic effect, reducing the need for preclinical experiments that directly measure vessel normalization parameters.

Continuous-fiber preform reinforcement of dental resin composite restorations.

OBJECTIVES: Direct-filling resin composites are used in relatively small restorations and are not recommended for large restorations with severe occlusal-stresses. The aim of this study was to reinforce composites with fiber preforms, and to investigate the effects of layer thickness and configurations on composite properties. It was hypothesized that fiber preforms would significantly increase the composite's flexural strength, work-of-fracture (toughness) and elastic modulus. METHODS: Glass fibers were silanized, impregnated with a resin, cured, and cut to form inserts for tooth cavity restorations. Also fabricated were three groups of specimens of 2mm x 2mm x 25 mm: a fiber preform rod in the center of a hybrid composite; a thin fiber layer on the tensile side of the specimens; and a thin fiber layer sandwiched in between layers of a hybrid composite. These specimens were tested in three-point flexure to measure strength, work-of-fracture and modulus. Optical and scanning electron microscopy were used to examine the restorations and the fiber distributions. RESULTS: Microscopic examinations of insert-filled tooth cavities showed that the fibers were relatively uniform in distribution within the preform, and the inserts were well bonded with the surrounding hybrid composite. Specimens consisting of a fiber preform rod in the center of a hybrid composite had a flexural strength (mean (SD); n=6) of 313 (19)MPa, significantly higher than 120 (16)MPa of the hybrid composite without fibers (Tukey's at family confidence of 0.95). The work-of-fracture was increased by nearly seven times, and the modulus was doubled, due to fiber preform reinforcement. Similar improvements were obtained for the other two groups of specimens. SIGNIFICANCE: Substantial improvements in flexural strength, toughness and stiffness were achieved for dental resin composites reinforced with fiber preforms. The method of embedding a fiber preform insert imparts superior reinforcement to restorations and should improve the performance of direct-filling resin composites in large restorations with high occlusal-loads.

Whole-gene APC deletions cause classical familial adenomatous polyposis, but not attenuated polyposis or "multiple" colorectal adenomas.

Familial adenomatous polyposis (FAP) is a dominantly inherited colorectal tumor predisposition that results from germ-line mutations in the APC gene (chromosome 5q21). FAP shows substantial phenotypic variability: classical polyposis patients develop more than 100 colorectal adenomas, whereas those with attenuated polyposis (AAPC) have fewer than 100 adenomas. A further group of individuals, so-called "multiple" adenoma patients, have a phenotype like AAPC, with 3-99 polyps throughout the colorectum, but mostly have no demonstrable germ-line APC mutation. Routine mutation detection techniques fail to detect a pathogenic APC germ-line mutation in approximately 30% of patients with classical polyposis and 90% of those with AAPC/multiple adenomas. We have developed a real-time quantitative multiplex PCR assay to detect APC exon 14 deletions. When this technique was applied to a set of 60 classical polyposis and 143 AAPC/multiple adenoma patients with no apparent APC germ-line mutation, deletions were found exclusively in individuals with classical polyposis (7 of 60, 12%). Fine-mapping of the region suggested that the majority (6 of 7) of these deletions encompassed the entire APC locus, confirming that haploinsufficiency can result in a classical polyposis phenotype. Screening for germ-line deletions in APC mutation-negative individuals with classical polyposis seems warranted.

Electrochemical characterization and immersion corrosion of a consolidated silver dental biomaterial.

A consolidated silver (CS) material, an alternative to dental amalgam, was studied for corrosion. Chemically precipitated silver particles were acid activated and pressure consolidated to a volume porosity of 25%. In selected tests comparisons were made between CS and melted and cast silver particles (MS), silver with a known mass fraction purity of 99.998% (FS), a silver-palladium alloy (SP). and a dispersed-phase amalgam (DA). Fusayama artificial saliva was used with controlled variations in pH, sulfide content, mucin content, and absorbed oxygen content. Electrochemical polarization, electrochemical impedance spectroscopy, and immersion methods were used. Results revealed differences in the zero current potentials E(I = 0) from forward polarization between CS and MS (or FS) in deaerated solution. By superposition of the cathodic polarization curves, the area for CS was increased by 7.3 times and was enclosed within an outer shell of material 5.5 microm thick. Polarization resistance was significantly the highest for SP, followed in order by MS (or FS) and CS or DA. With scanning electron microscopy, CS was shown to be significantly more susceptible than MS to long-term immersion corrosion. The modeled equivalent electrical circuits for CS and DA involved a double layer capacitance, a charge transfer resistance, and an element attributed to adsorption. The active pore depth for CS from the transmission line model for porous solids revealed satisfactory agreement with polarization results. It is concluded that the corrosion susceptibility of CS in Fusayama solution, while similar to that for DA, is greater than it is for MS.

In vitro tarnish and corrosion of a consolidated silver material for direct filling applications.

OBJECTIVES: A consolidated silver (CS) material, composed of acid activated silver particles has been developed for direct filling applications. The hypothesis to be tested was that the tarnish discoloration and immersion corrosion of CS was similar to that of a dispersed phase amalgam (DA). METHODS: Disk-sized samples of CS and DA were prepared. CS contained a volume porosity of 25%, comparable to the material prepared for clinical uses. CIE L(*)a(*)b(*) colorimetry was used to evaluate tarnish discoloration, while solution analysis was used to evaluate corrosion susceptibility. Surfaces following tarnish and corrosion were characterized with SEM-EDS and X-ray diffraction. Fusayama solution, defined as an artificial saliva composed of NaCl, KCl, CaCl(2).2H(2)O, NaH(2)PO(4).H(2)O, Na(2)S.9H(2)O, and urea at component concentrations of (6.8, 5.4, 5.4, 5.0, 0.021 and 16.7mmol/l, respectively, was used with controlled variations in sulfide-content. Clinically relevant sulfide contents below, equal to, and above the original Fusayama concentration were used. Intermittent exposures to air and saliva and continuous immersions were performed for tarnish discoloration, and agitated continuous immersions in 0.1mol/l NaCl+0.1mol/l lactic acid were performed for corrosion testing. The effects on tarnish discoloration by adding mucin and other salivary proteins to saliva were studied. RESULTS: The total color vector change (DeltaE(ab)(*)) for CS was significantly greater than for DA. Intermittent air and saliva exposures significantly increased DeltaE(ab)(*) for CS relative to continuous immersions. The rate of tarnish discoloration for CS increased with sulfide concentration. With adding protein to saliva, DeltaE(ab)(*) for CS significantly decreased. Mucin partly inhibited the discoloration from sulfide. The morphology of the tarnished products depended upon the testing method. For CS continuously immersed in sulfide- and protein-free saliva, a porous AgCl layer intermixed with black corrosion products, taken to be Ag(2)O, formed, while intermittent exposures to air and sulfide-containing saliva formed a continuous, dense and adherent layer identified as Ag(2)S. The concentrations of released silver from CS and DA were similar. However, DA also dissolved concentrations of copper and tin, changed solution pH, and grossly affected solution color, none of which occurred with CS. SIGNIFICANCE: CS is most susceptible to tarnish discoloration in protein-free, sulfide-containing saliva under alternating wet and dry conditions. The release of silver from CS is not significantly different to the release of silver from DA.

Comparative mechanical property characterization of 3 all-ceramic core materials.

PURPOSE: The biaxial flexural strength and fracture toughness for 3 representative types of ceramic core materials were studied to (1) ascertain the ranking of the 3 ceramic types for strength and toughness, and (2) provide clinicians with more information to predict clinical outcomes. The former aim was deemed important in view of the importance of flaw size in the relationship between failure stress and fracture toughness of brittle materials. MATERIALS AND METHODS: The 3 representative ceramic types included a leucite-reinforced glass, a glass-infiltrated sintered alumina, and a high-purity, high-density alumina. The biaxial flexural strength was measured with the piston-on-3-ball method. The plane-strain fracture toughness was measured with the short-bar chevron-notch method. RESULTS: The biaxial flexural strengths of the high-purity, high-density alumina and glass-infiltrated sintered alumina ceramic core types were significantly higher than that of the leucite-reinforced glass ceramic type. The glass-infiltrated sintered alumina was significantly higher in fracture toughness than the high-purity, high-density alumina type, which was significantly higher than the leucite-reinforced glass. CONCLUSION: All materials surpassed the minimum strength requirement outlined by the International Standards Organization, and they also had similar strength variability according to their Weibull moduli. The glass-infiltrated sintered alumina and the high-purity, high-density alumina types were significantly stronger and tougher than currently used core materials. However, while the glass-infiltrated sintered alumina had a higher fracture toughness than the high-purity, high-density alumina, it had a lower flexural strength.

Study of devitrification of Dicor glass.

The nucleation and crystallization of tetrasilicic fluormica crystals in the Dicor group of glass ceramics is not as well understood as the crystallization sequence of trisilicic mica in the Macor group of glass ceramics. The main aim of this investigation was to obtain kinetic data of crystallization and to examine the devitrification process at different stages of heat treatment during non-isothermal heating. The kinetic parameters, such as the activation energy, Ec, the reaction order, n, and the frequency factor, v, for the devitrification reaction were computed using the Johnson-Mehl-Avrami (JMA) equation and the data from differential thermal analysis (DTA). The crystallization at different stages of devitrification was evaluated by scanning electron microscopy (SEM) observations, and Fourier transform infrared (FTIR) spectroscopy with KBr-reflectance technique. All DTA curves at different heating rates showed a single exothermic crystallization peak, just above the glass transition temperature in the temperature range of 745-850 degrees C. Linear relationships between the logarithm of heating rate and the reciprocal of temperature, and the logarithm of temperature rise and the reciprocal of temperature were observed. The computation of kinetic parameters gave the values for activation energy, Ec = 203 kJ mol-1, the reaction order n = 3.4 +/- 0.20 and the frequency factor v = 2.88 x 10(11) s-1. SEM observation showed precipitation of crystals in the DTA run which were considerably finer (approximately 0.1 micron) than the block shaped mica plates (approximately 4 microns) observed in the sample subjected to recommended non-isothermal-isothermal heating cycle. The FTIR spectra of beyond the exothermic peak DTA run samples, and the completely cerammed samples showed two additional peaks at wave numbers of 705 and 671 cm-1 compared with the ascast glass and the samples heated before the onset of the exothermic peak. Similar peaks in FTIR spectra also appeared from MgF2- powder at the same wave numbers. Based upon these results, it is proposed that during non-isothermal heating a spinodal decomposition of glass matrix occurs, which is followed by the exothermal precipitation of round tetrasilicic fluormica crystals by a cellular precipitation mechanism.

Inhibition of protein kinase C mu by various inhibitors. Differentiation from protein kinase c isoenzymes.

Various inhibitors were tested for their potential to suppress the kinase activity of protein kinase C mu (PKC mu) in vitro and in vivo. Among the staurosporine-derived, rather selective PKC inhibitors the indolocarbazole Gö 6976 previously shown to inhibit preferentially cPKC isotypes proved to be a potent inhibitor of PKC mu with an IC50 of 20 nM, whereas the bisindolylmaleimide Gö 6983 was extremely ineffective in suppressing PKC mu kinase activity with a thousand-fold higher IC50 of 20 microM. Other strong inhibitors of PKC mu were the rather unspecific inhibitors staurosporine and K252a. Contrary to the poor inhibition of PKC mu by Gö 6983, this compound was found to suppress in vitro kinase activity of PKC isoenzymes from all three subgroups very effectively with IC50 values from 7 to 60 nM. Thus, Gö 6983 was able to differentiate between PKC mu and other PKC isoenzymes being useful for selective determination of PKC mu kinase activity in the presence of other PKC isoenzymes.

Effect of food and oral simulating fluids on structure of adhesive composite systems.

This work evaluates the degradation of three adhesive/composite systems (Tenure/Marathon One. Scotchbond Multi-Purpose/Z100 and Optibond/Herculite XRV) upon immersion in 75% ethanol solution and in an artificial saliva (Moi-Stir). Shear bond strength (SBS) and diametral tensile strength (DTS) specimens were employed for this study. For the SBS specimens, the bonded interface and composite were exposed to food and oral simulating fluids at 37 degrees C for up to 30 days. A similar control series was stored in air. DTS specimens were stored in 75% ethanol at 37 degrees C for up to 30 days. The SBS specimens were sheared to failure. Small quantities of bonding resin were removed from the tooth side of the fractured surface and from the non-fractured fractured end of the composite for Fourier transform infrared microscopic evaluation. Similar scrapings were taken from DTS specimen surfaces. The infrared absorbance intensity (AI) of the major peaks was measured as a function of storage time and ratioed against the aromatic C = C (1609.4 cm-1) peak. The data were analysed using ANOVA and the Tukey LSD test. The AI of major peaks was similar for the materials stored either in air or in Moi-Stir for all testing periods. Storage in ethanol caused the AI of aliphatic C = C (1638 cm-1) and of O-H (approximately 3500 cm-1) bonds to significantly decrease (30-50%) for specimens of bonding resin while the AI of C = O bonds (1730 cm-1) increased (60-120%).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of food and oral simulating fluids on dentine bond and composite strength.

The effect of up to 30 days' immersion in 75% ethanol solution and in an artificial saliva (Moi-Stir) on the dentine shear bond strength (SBS) of three adhesive/composite systems (Tenure/Marathon One, Scotchbond Multi-Purpose/Z100 and Optibond/Herculite XRV) was evaluated. Two control series were stored either in 100% humidity or in air. Diametral tensile specimens (DTS) of the composites studied were stored in 75% ethanol for up to 30 days. The fracture mode and morphology of the failure interface were examined by scanning electron microscopy (SEM). Data were analysed using ANOVA and the Tukey LSD test. The SBS for all systems stored in Moi-Stir (24.8 +/- 3.0 MPa) and air (28.3 +/- 3.0 MPa) was not influenced by length of storage. Microscopic (SEM) examination of the debonded air, and Moi-Stir stored specimens showed that failure had primarily occurred through the dentine. Significant decreases (30-50%) in the SBS of all systems occurred after immersion in 75% ethanol. There was no significant difference among brands. The DTS of the composites showed significant decreases as a function of ethanol exposure. Marathon One and Herculite XRV showed significantly lower DTS after 14 days' storage while Z100 showed no reduction in DTS until after 30 days. The decrease in both SBS and DTS after storage in ethanol was a function of the square root of time (P < 0.001) and followed Fick's laws of diffusion. Ethanol diffusivity was approximated as 1.8 x 10(-6) cm2 s-1 for both SBS and DTS specimens, suggesting that alcohol attack in SBS specimens occurred primarily in the composite system.(ABSTRACT TRUNCATED AT 250 WORDS)

Heats of reactions between dentine bonding agents and tooth components.

The heat of reaction of dentine bonding agents alone and dentine bonding agents with dentine, hydroxyapatite and collagen were measured using a differential scanning calorimeter (DSC) in the isothermal mode. The bonding agents were Scotchbond and Panavia Ex adhesives, and GC Fuji-II glass ionomer cement. The heat of reaction for Scotchbond and Panavia Ex bonding adhesives were 44.3 and 6.9 mcal/mg, respectively. Furthermore, results support the view that the glass ionomer cements adhere to tooth structure by chemical bonding.

Leaching from glass ionomer cements.

This study compared the electrical conductivities, pH and leached ion (F-, Ca, Al, Si) concentrations in supernatant liquids obtained from four glassionomer cements, a buffered ionomer cement, a polycarboxylate cement and a zinc phosphate cement, at three different levels of settings. The result indicated that the measured parameters are highest for the unset condition of cements and decreases as the set condition is approached, except for pH, which shows the opposite trend. Two pulp sensitive glassionomer cements, Chem Bond and Ketac Cem showed high Ca:F ratios as well as high Ca and F concentrations. Further, it is suggested that the cytotoxicity of leached F-, Si, Al and Zn at high concentration and at low pH may induce sensitivity in tooth structure.

Fracture toughness, diametrical strength, and fractography of amalgam and of amalgam to amalgam bonds.

Chevron-notch fracture toughness, diametrical tensile strength and fractography were evaluated for bulk amalgams and for bonds formed between new and 1-day-old amalgams of the same type. Three types of bonded specimens were prepared: 1) by mechanically roughening the 1-day-old amalgam with 600-grit paper; 2) using a new mercury-rich amalgam; and 3) using a bonding resin, either 4-META or a phosphate ester monomer. Similar values in bond properties were obtained with all bonding techniques for two commercial dispersed-phase bonded amalgams, one of which contained palladium; however, bulk fracture toughness of the palladium-containing amalgam was significantly less than for the palladium-free amalgam. This result reveals that the bonding of amalgam to amalgam, at least for these two amalgams, is a surface-related phenomenon, and thus, the traditional reporting of bonding properties as a percentage of bulk properties loses meaning. Short-rod geometry was more representative of the interfacial bond properties since these samples fractured within the interfacial bonds, while diametrical strength samples often fractured slightly away from the interface. The use of bonding resins did not improve bond fracture toughness for either amalgam, while the diametrical strength improved for one of the amalgams. The use of mercury-rich amalgam significantly improved the fracture toughness over all other techniques for one amalgam while proving to be similar to a 600-grit preparation for the second amalgam.(ABSTRACT TRUNCATED AT 250 WORDS)

Copper-, indium-, tin-, and calcium-fluoride admixed amalgams: release rates and selected properties.

A conventional (Minimax), two single-particle high-Cu (Summalloy and Aristaloy CR), and two dispersed-phase (Cluster and Phasealloy) amalgam alloys were each admixed with 0.5 wt% of CuF2, InF3, SnF2, and CaF2, and evaluated for F-, Cu, and Sn release, as well as for corrosion resistance, microstructure, and compressive strength. Over a 43-week interval, only Cluster revealed somewhat of a sustained F- release in artificial saliva. A ranking for F- release was Cluster (highest), Summalloy, Phasealloy, Minimax, and Aristaloy CR. The effectiveness of the F- compounds in releasing F- followed CuF2 (highest), SnF2, InF3 (1.0%), InF3, and CaF2. Amalgams with admixed CuF2 released both the most Cu and increased Sn. For three amalgams, CaF2 admixtures also increased the Cu release. Constant-potential coulometry distinguished among the different fluoride amalgams. Only Minimax revealed a significant reduction in compressive strength with two admixtures. Microstructural analysis revealed an increased pore distribution around the Ag-Cu dispersed particles, and it was assumed that the F- particles were contained within the pores, since SEM, EDS with a low element detector, and ESCA were all unable to detect the F- particles.

Fracture toughness and fractography of dental cements, lining, build-up, and filling materials.

The plane strain fracture toughness (K1c) at 23 degrees C and the fractography of zinc phosphate and zinc polycarboxylate cements, buffered glass ionomer liner, amalgam alloy admixed glass ionomer build-up material, and glass ionomer, microfilled and conventionally filled bis-GMA resin composite filling materials were analyzed by elastic-plastic short-rod and scanning electron microscopy methodologies. Results indicated that significant differences occurred in their K1c's from the lowest to the highest in the following groups of materials, (i) buffered glass ionomer, (ii) zinc phosphate, glass ionomer, zinc polycarboxylate, and alloy mixed glass ionomer, (iii) microfilled resin, and (iv) conventionally filled resin. All materials except the microfilled resin, which fractured via crack jumping, fractured via smooth crack advance. Filler debonding without any crack inhibiting process was related to materials with low K1c values. The incorporation of either buffering compounds or alloy particles into glass ionomer had no beneficial effect upon fracture toughness. This was in contrast to microfilled and conventionally filled resins where either crack blunting or crack pinning processes, respectively, were likely involved with their increased K1c's. For microfilled resin, distinct radial zones positioned around the chevron apex and characterized by plastically deformed deposited material were related to distinct crack jumps that occurred in the load versus displacement behavior. Finally, for the two remaining materials of zinc phosphate and polycarboxylate, particle cleavage and matrix debonding for the former and shear yielding for the latter occurred.

Microscopy analysis of dental titanium casting investment materials.

Scanning electron microscopy (SEM) analysis and qualitative energy dispersive x-ray microanalysis (EDS) of investment materials for dental titanium casting were performed. Two commercial investment materials, Ohara and Castmatic, and an experimental zirconia material were analyzed. The microstructural constituents and the unfired and fired structures were included. Larger refractory particles and matrix embedding smaller particles were observed with each material. Detection of aluminum, silicon, magnesium, zirconium and oxygen provided a basis to reason the presence of alumina (Al2O3), silica (SiO2), magnesia (MgO), and zirconia (ZrO2). Hence, Ohara contained quartz and an alumino-silicate, Castmatic contained magnesia and quartz and experimental zirconia contained zirconia and an alumino-silicate, taken to be kyanite, as components providing refractoriness and expansion. Even though unequivocal detection of phosphorous in the spectra for Ohara was not obtained (P K alpha = 2.013 keV; Zr L alpha = 2.042 keV), an emission peak at 2.0 keV was taken to be due to P and related, along with MgO, to bonding by magnesium phosphate. For Castmatic, unfired strength was thought to be due to calcium chloride and calcium silicate and fired strength to forsterite, (2MgO.SiO2). Detection of calcium and chlorine also suggested bonding of experimental zirconia via calcium chloride. Extensive microcracking occurred around refractory particles and through matrix in experimental zirconia which is likely to have resulted from the firing of kyanite to 1400 degrees C, to the monoclinic to tetragonal transformation of any unstabilized ZrO2, or to the thermal expansion mismatch between kyanite and matrix.

Surface analysis of tarnished dental alloys.

Six crown and bridge alloys ranging in nobility between 25-63 wt % (18-45 at %) were analyzed by optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and secondary ion mass spectroscopy (SIMS), as well as by L*a*b* colorimetry before and after in vitro tarnishing in artificial saliva with and without additions of 0.00016, 0.016, and 1.6 % Na2S with a rotating wheel apparatus. All alloys except the lowest of 18 at % changed colors to about the same degree after 72 h of tarnishing. All alloys decreased in L*, while increased in both a* and b*, thus appearing darker and with increased redness and yellowness. This was due to localized darkening and to other products. For all alloys except one, saliva without sulfide promoted color changes more severe than for saliva with 0.016 % Na2S. For the most part, analysis by EDS was unable to detect differences between the tarnished films and the as-polished surfaces. SIMS analysis, however, showed changes in the substrate ion (Cu, Ag, Pd, and In) peak intensities. In most cases the intensities decreased and with the decrease greater with the sulfide-free saliva than with sulfide-containing. This indicated that sulfide promoted insoluble deposition of products. Changes in the Ag, Pd, and In peak intensities followed much the same pattern as with Cu. The as-polished surfaces, even though carefully prepared, showed much contamination in the form of organics, namely C, CH, N, NH, O, CHN, CN, as well as from Na, K, Ca, Si, S, Cl, and others. Most tarnished surfaces showed large increases in Na, K, and Ca, and with the sulfide-free saliva being more severe in this regard. The mass spectrum also showed peaks with atomic mass units in the range 55-58 related to only some of the tarnished surfaces.

Corrosion of dental burs in sterilizing and disinfecting solutions.

Potentiodynamic anodic polarization, SEM, and energy dispersive microanalysis techniques were used to determine electrochemical aggressiveness of disinfecting and sterilizing solutions on carbide and stainless steel burs. The importance of galvanic cell formation in carbide burs caused by mixed metal coupling was examined. The following conclusions were reached. 1. Anodic polarization methods are an effective means for discriminating among the relative corrosiveness of sterilizing and disinfecting agents on dental instruments, particularly dental burs. 2. The relative degree of corrosiveness on stainless steel burs shows Omni II and Omnicide solutions the best, Sterall and Sporicidin solutions the poorest, and Glutarex solution intermediate. Omnicide and Glutarex solutions show the least degree of corrosiveness on the carbide burs. 3. SEM analysis of ground, polished, and treated surfaces shows corrosion deposition over the soldered joint of the carbide burs. The stainless steel shank is a cathodic component of a three-way galvanic cell, whereas the silver soldered joint is an anodic component.